1. Field of the Invention
The present invention relates to the field of communications. More particularly, the present invention relates to improving reliability when adding layer three routing to layer two networks.
2. Background Information
FIG. 1 illustrates an example of today's networking environment in which layer two networks are provided with layer three routing. In today's networking environment, a customer edge device 10 connects to a layer two switch 12, such as an ATM switch or a frame relay switch. The switches 12 are interconnected with interoffice trunks 14. The connection 16 between the switch and the customer edge device 10 can be any known interface.
In an asynchronous transfer mode (ATM) example, a permanent virtual connection (PVC) 18 is configured from the ATM switch port connecting to the customer edge device 10 to a trunk 15 terminating at the far end of the switch 12. The trunk 15 is similar to the other trunks 14 shown, except, the trunk 15 is partitioned. The partitioning is required to separate a user-network interface (UNI) e.g., an Internet protocol (IP) interface, from the standard layer two trunk group. At least one partition is required for the standard ATM trunks, and another partition is required for each IP interface that is defined. Complex provisioning and associated administrative burden are required to partition the trunk 15.
The IP interface across the trunk 15 is defined between the switch 12 and a platform 20, such as an Alcatel 7670 RSP (routing switch platform), available from Compagnie Financiere Alcatel of France. The defined IP interface on the ATM trunk 15 uses standard ATM encapsulation. The defined IP interface must also specify a virtual path identifier/virtual channel identifier (VPI/VCI) of the PVC connection 18, associated with the IP service, to the customer edge device 10.
The platform 20 includes layer two switching capabilities and layer three switching capabilities. In today's multi service platforms 20, the layer two portion is independent from and isolated from the layer three portion. Typically, a layer three port 22 of the multi service platform 20 terminates the UNI connection 15.
A problem associated with the current configuration is that when the UNI connection 15 (either the link or a port) fails, the layer two network will not re-route a circuit to the multi service platform 20 because the layer two network only extends to the connection 15. In other words, the PVC 18 terminates on the layer two switch 12, and not on the platform 20. Thus, no layer two protection is available for the trunk 15 between the switch 12 and the platform 20. If the trunk 15 fails, all customers using the link 15 would be out of service.
Current solutions addressing the single point of failure problem include dual homing from a customer site 10 to two different platforms 20. In this case, when one connection fails, the other connection can maintain connectivity. This approach, however, consumes too many network resources by requiring both paths to be permanently maintained, adding significant complexity to the provisioning and maintenance procedures for this service.
Another solution reduces the length of the connection between the switch 12 and the platform 20 by deploying the switches 12 and platforms 20 within the same central office. Thus, the connection 15 becomes an intra-central office connection. This solution, however, increases the overall switch deployment cost and is still subject to a single point of failure.
Thus, a solution is needed to address the single point of failure problem and the complexity of provisioning problem without increasing consumption of network resources.